I used to size deck joists and beams by what I guessed would pass muster with the local building official. After submitting my deck plans, I’d keep my fingers crossed that they’d be approved, hedging my bets by sizing the joists larger than I guessed they’d need to be and reducing beam spans by placing footings closer together. Because my framing plans were rarely questioned, I figured I was doing something right.

But during a discussion about deck framing with a building official, I realized that he ran into the same challenge. Without tables for deck framing in the code, he didn’t have a simple resource to determine whether I and other deck builders sized joists and beams properly. One solution, of course, would have been to require an engineer to design the framing, but thankfully most officials were reluctant to add that expense to our jobs. When I asked one official how he determined whether a joist could span the designed distance, he said he used floor-joist tables intended for interior floor framing. But those tables don’t have wet service or incising factors applied, so they aren’t applicable for deck design.

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